Cryogenic vacuum pumps, or cryopumps, currently available generally follow a common design concept. A low temperature array, usually operating in the range of 4 to 25 K., is the primary pumping surface. This surface is surrounded by a higher temperature radiation shield, usually operated in the temperature range of 60 to 130 K., which provides radiation shielding to the lower temperature array. The radiation shield generally comprises a housing which is closed except a frontal array positioned between the primary pumping surface and a work chamber to be evacuated.
In systems cooled by closed cycle coolers, the cooler is typically a two-stage refrigerator having a cold finger which extends through the rear or side of the radiation shield. High pressure helium refrigerant is generally delivered to the cryocooler through high pressure lines from a compressor assembly. Electrical power to a displacer drive motor in the cooler is usually also delivered through the compressor.
After several days or weeks of use, the gases which have condensed onto the cryopanels, and in particular the gases which are absorbed, begin to saturate the cryopump. A regeneration procedure must then be followed to warm the cryopump and thus release the gases and remove the gases from the system. As the gases evaporate, the pressure in the cryopump increases, and the gases are exhausted through a relief valve. During regeneration, the cryopump is often purged with warm nitrogen gas. The nitrogen gas hastens warming of the cryopanels and also serves to flush water and other vapors from the cryopump.
Nitrogen is the usual purge gas because it is inert, and is available free of water vapor. It is usually delivered from a nitrogen storage bottle through a fluid line and a purge valve coupled to the cryopump.
After the cryopump is purged, it must be rough pumped to produce a vacuum about the cryopumping surfaces and cold finger to reduce heat transfer by gas conduction and thus enable the cryocooler to cool to normal operating temperatures. The rough pump is generally a mechanical pump coupled through a fluid line to a roughing valve mounted to the cryopump.
Control of the regeneration process is facilitated by temperature gauges coupled to the cold finger heat stations and by pressure gauges. The temperature and/or pressure sensors mounted to the pump are coupled through electrical leads to temperature and/or pressure indicators.
Although regeneration may be controlled by manually turning the cryocooler off and on and manually controlling the purge and roughing valves, a regeneration controller is used in more sophisticated systems. Leads from the controller are coupled to each of the sensors, the cryocooler and motor and the valves to be actuated. In U.S. Pat. No. 4,918,930 entitled "Electronically Controlled Cryopump" by Peter Gaudet, et al., the entire teachings of which are incorporated herein by reference, regeneration control electronics are integrally mounted to the cryopump.